MT can't ping freeradius's ip

Dear all

i have a freeradius running on a box i connected it to the wan side of MT.
i have setup radius - service - ppp - IP:192.168.1.100 (ip of the freeradius box) and
the shared secret .

I cannot ping the freeradius box although i can ping it from the same switch which is connected to , but not from the ping of MT.

i have setup all the configuration right aaa & radius .

the question is how can i ping the freeradius ip from MT
any help please?

10x in Advanced